the main reason that made red john kill jane's family is because jane insulted and disrespected red john in public, we understand of this that red john is proud, sadistic and enumerate any evil characteristics. it is like a message for jane "Don't you ever show irreverence to someone you don't know".
apparently, in S1E1 jane described brett as "ghoul" which the red gohn is but the interesting thing watching partridge's face expressions, like he says don't mess with me he hated that jane humiliating him every time.

just a thought ^-^